1. Field of the Invention
This invention relates to an apparatus for processing a video signal in a video tape recorder, and more particularly to an apparatus for processing a video signal, in which the chrominance signal is processed in a digital signal form.
2. Description of the Prior Art
Generally, in the widely used commercial color VTRs, the luminance signal is converted to a frequency modulated luminance signal (FM luminance signal, hereafter) positioned at upper band in the recordable frequency band, and the chrominance signal is frequency converted to be lower in frequency band than the FM luminance signal. The FM luminance signal and the down-converted chrominance signal are multiplexed, and the multiplexed signal is recorded on the magnetic tape.
In the reproducing mode, the multiplexed signal reproduced from the magnetic tape is separated to the FM luminance signal and the down-converted chrominance signal. The FM luminance signal is demodulated to be the original luminance signal, and the down-converted signal is frequency-converted to the original chrominance signal.
In the conventional signal processing method as described above, the chrominace signal needs to be executed various complicated signal processing. This makes it difficult to realize a simple and small-sized signal processing circuit.
For example, in the commercial VTR the so-called jutter is caused by the variation of the relative speed between the magnetic tape and the rotary magnetic head, due to the performance variation of the servo system or the stretched magnetic tape. The jitter causes phase fluctuation of the reproduced chrominance signal, and therefore not-uniformity in color of the reproduced color picture. To avoid the phase fluctuation of the chrominance signal, an automatic phase control (APC) system is usually provided in the reproducing side chrominance signal processing block. However, the APC system makes the whole circuit very complex in configuration, large in size, and expensive in cost.
Further, in the adimus recording method without guard tracks, a comb filter is employed as a one horizontal line delay device to reduce the cross talk signals from the adjacent track in the reproducing mode. This comb filter is usually comprised of a glass delay line which is large in size and expensive. Accordingly, the signal processing circuit cannot be made compact and inexpensive.
FIG. 1 is a block diagram of the main portion of a typical conventional VTR for explaining the luminance and chrominance signal processings. In the recording signal processing block, a composite video signal applied to an input terminal 1 is separated to the luminance signal and the chrominance signal by a low-pass filter 2 and a band-pass filter 3. The luminance signal is frequency modulated by a frequency modulator 4 and the obtained FM luminance signal is supplied to a mixer 9. The chrominance signal is converted to a low frequency band signal (down-converted chrominance signal) by a balanced modulator 5 with a local oscillator 6 and a low-pass filter 7. The down-converted chrominance signal is processed, or phase-shifted, for example, by a recording signal processor 8, and supplied to the mixer 9. The FM luminance signal and the processed down-converted chrominance signal are multiplexed by the mixer 9. The multiplexed signal is recorded on a recording medium 10 such as a magnetic tape.
In the reproduced signal processing block, the reproduced signal from the recording medium 10 is separated to the FM luminance signal and the down-converted chrominance signal by a high-pass filter 11 and a low-pass filter 12. The FM luminance signal is demodulated to the original luminance signal by a demodulator 13 and the original luminance signal is inputted to a mixer 18. The reproduced down-converted chrominance signal is executed. by a reproduced signal processor 14 with processes such as phase shifting, automatic phase controlling, and comb filtering, and converted to the original chrominance signal by a balanced modulator 15 with a local oscillator 16 and a band-pass filter 17. The original chrominance signal is mixed with the original luminance signal by the mixer 18 to be a composite video signal which is supplied to an output terminal 19.
In view of the above, since the above described complicated chrominance signal processing is achieved in analog signal form, the circuit configuration is complicated and large-sized.